Final answer:
The correct answer to which DNA strand can form a duplex by pairing with itself is option b) 5'-AAGCCGTT-3', since it follows the base pairing rules and reads the same backward and forward, allowing for proper self-complementation.
Step-by-step explanation:
The student is querying about DNA complementarity, which refers to how DNA strands form bonds in accordance with specific base pairing rules. In DNA, adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G). Given a sequence on one strand, the complementary DNA strand is assembled by matching each base with its partner, ensuring A pairs with T and C pairs with G, while the strands run antiparallel to each other. For example, if one sequence is 5'-AATTGGCC-3', the complementary strand would be 3'-TTAACCGG-5'. Similarly, when considering a self-pairing DNA duplex, we are searching for symmetry within the same strand that would allow it to fold onto itself with proper base pairing.
For the options given:
a) 5'-AAGCCGAA-3' cannot pair with itself because the bases are not complementary in reverse (G with C, C with G, and so on).
b) 5'-AAGCCGTT-3' can pair with itself because the sequence reads the same backward and forward with complementary bases.
c) 5'-AAGCGCAA-3' cannot pair with itself due to a similar issue as in option a.
d) 5'-AAGCGCTT-3' also cannot pair with itself as the bases are not complementary in reverse.
Therefore, the correct answer is option b) 5'-AAGCCGTT-3', as it is the only sequence that can form a DNA duplex by pairing with itself at each position.